Few Questions about aquariums.?

I have a nearly established (4 month old) 10g aquarium with one fantail goldfish in it. I am moving her up to a 29g when i get a filter for the tank i was given and get some decorations. I was wondering if, after i've moved her, will the tank be able to immediately have tropical fish in it, or do i have to take it down and restart (like from the move from goldy to tropicals) or can I just keep everything the way it is now, except get a heater and just plop the fish in the exsisting water. Another question is, Is there a point in using Easy Balance by tetra if I change the water every single week anyway? I bought it and have been using it, but you are supposedly supposed to be able to not change the water for up to 6 mos. at a time, but there's no WAY i would not change my goldfishes water for 6 mos. So is there a point in using it, like is it still providing the benefits of helping the bacteria grow and reducing the phosphates or whatever?